Well, don’t you know
I’m gonna skate right through
Ain’t nobody do it but me
Nobody but me -The Human Beinz
If you’re only a casual watcher of the night sky, you might have no idea what the brightest stars are. Sure, if you’re in the northern hemisphere, you probably recognize the Big Dipper,
the bright stars in the constellation Orion (particularly the “belt”),
the Pleiades, otherwise known as the Seven Sisters,
and Cassiopeia, the giant “W”.
And if you’re farther south, you probably know the extraordinarily bright Canis Major (big dog),
as well as the Southern Cross and the two Pointer stars, which help you find the South Celestial Pole.
If you’ve been coming by for a while, you probably also know that we classify stars into seven different types, based on how intrinsically bright and blue they are: O B A F G K and M.
The brightest stars are also the rarest ones — only about 0.2% of stars are O or B stars — and while you might have heard that our Sun, a G-type star, is pretty common, we’re actually brighter than about 95% of the stars in the sky! Why’s that? Because 3 out of every 4 stars are M-stars: red dwarfs.
But this doesn’t mean that the ones that appear brightest have to actually be intrinsically bright; they could just be close to us! So what’s more important, brightness or closeness? Let’s learn what the brightest stars are! (Not including the Sun, obviously!)
Sirius, found in the constellation of the big dog (Canis Major), is by far the brightest star in the night sky. It’s close — only 8.7 light years away — it’s bright, being an A star, and it’s so bright that it often outshines many of the planets.
But the second brightest? Unless you live in the South of Africa, South America, or New Zealand, you probably don’t know well at all. (Those are the only locations where it’s always visible.)
Although it’s less than half as bright as Sirius, Canopus is over 300 light years away! But Canopus is quite far south, sort of isolated in the sky from other bright stars, and practically invisible to the Northern Hemisphere.
But I bet you know #3, even if you’ve never seen it.
Alpha Centauri, at just 4.4 light years away, is the same type of star as our Sun. But it’s the closest bright star to us, and (combined with its binary companion) appears to be the 3rd brightest star in the sky! We’ve already seen this, of course: Alpha Centauri is the brighter of the two “pointer” stars that help you find the South Celestial Pole!
You’ve got to be asking yourself, then, what the deal is with that “other” pointer star?
Believe it or not, Beta Centauri, the slightly dimmer, blue one, is #10 in brightness in the sky! But it couldn’t be more different. One of the most intrinsically bright stars, Beta Centauri is one of the brightest B-stars we have, and is located (depending on who you ask) up to 500+ light years away!
But what about those of us stuck up here in the Northern Hemisphere? What do we get?
Well, we’ve got the orange giant, Arcturus, which is well known for being a “runaway” star, not gravitationally bound to any of the stars around it, and coming in at #4 in brightness in the night sky. (Being a giant star, it matters less that it’s a cool, K star.)
And in the Summer, the Northern Hemisphere gets the following constellation:
The Summer Triangle! Consisting of Vega, the #5 star, Altair (#12), and Deneb (#19) — all blue A stars — you’ll know it when you see it.
But what about those constellations you know so well? Do they have anything worth mentioning? Well, the Big Dipper’s brightest star only comes in at #33, and Cassiopeia’s brightest only lands at #67. But Orion is a true gem.
The brightest blue star, Rigel, is a whopping 770 light years away: a blue supergiant — a B-star — and the sixth brightest overall. The super bright red star is Betelgeuse, the red supergiant — an M-star — 640 light years away, and the eighth brightest star in the sky. And on the same side of the belt as Betelgeuse is Bellatrix (thanks, @1 and @2), which comes in at #27, pretty impressive in its own right!
But Orion’s belt also features three ultra-bright, blue stars.
Mintaka, Alnilam and Alnitak are all blue supergiants. Mintaka is actually a double star, although is less remarkable at “only” #62, which still makes it brighter than all the stars in Cassiopeia! Alnilam and Alnitak, however, weigh in at #30 and #31 in brightness, respectively.
While Mintaka and Alnilam are (primarily) bright B-stars, Alnitak is the rarest (and bluest) of all the star types: a Class O-star!
This isn’t all of them, of course, but those are some of the more remarkable bright stars in the night sky; some are cool, some are hot, some are blue (or UV) and some are red, some are near and normal, some are distant and spectacular. But all of them give off light that travels years through space, reaches our eyes, and appears as just a slightly brighter point to us than the rest of space around it. And those are our brightest stars!